1. Field of the Invention
The present invention relates to method and apparatus for controlling time base in a system for reading information recorded on a record medium such as a record disc or recording tape, and more specifically to time base control method and apparatus for use in a system for playing back video and/or audio signal recorded on the recording medium.
2. Description of Background Information
In a video disc player for example, a time base control method is adopted in which time base is coarsely adjusted by controlling the rotational speed of a spindle motor for rotating the recording disc, so as to control a relative speed between the recording disc and an information reading point of a pickup operating as a signal reading means. At the same time a fine adjustment of the time base is effected by supplying a playback signal obtained by the pickup to a variable delay element. Owing to the fall in price of memory devices, it has become increasingly frequent to adopt a method in which a memory is employed as the variable delay element for the fine control, a pulse train signal is generated in synchronism with the time base variation of the playback signal, and the playback signal is written in the memory device by using this pulse train signal, and subsequently read out from the memory device by means of a reference pulse signal which has a stable frequency.
With conventional time base control systems, however, if the jump operation is executed with a CLV (constant linear velocity) disc, a disturbance is generated in the phase difference between write and read reset pulses since the reproduced video signal becomes discontinuous. As result, there arises a shortcoming that the values in write and read address counters of the memory device approach to each other, so that the time base correction is not performed properly.